MEMOIR XXX.] ON BURNING GLASSES AND MIRRORS. 



441 



brought about by a large convex lens which the direct 

 rays of the sun are wholly inadequate to produce. 



A very brilliant beam may possibly break up a given 

 combination, which a far greater quantity of light, acting 

 through a long period, might be inadequate to touch. 

 Sir R. Kane states that he, with M. Dumas, could remove 

 two atoms of hydrogen from acetone by the action of 

 chlorine in the sunshine at Paris, but in Dublin only 

 one. 



In Fig. 90, a is a convex burning -lens supported in 

 ribbed frame, b b ; there is at c a second lens to hasten 



Pig. 90. 



the convergence ; dd, a cir- 

 cular arc for directing the 

 lens towards the sun ; e g, 

 a stand on which objects 

 may be exposed to the fo- 

 cal point, f. It is carried 

 by a stout bar, m n, attached to the frame. 



By this instrument I endeavored to collect a series 

 of facts which might set this part of the question in 

 its true light. The lens a was of very fine and thin 

 French plate -glass, twelve inches in diameter in the 

 clear. Its goodness was such that on a fine day plat- 

 inum might be melted in its focus. It was ground 



